Power transistors commonly employed in automotive and industrial electronics require a low on-state resistance (Ron), while securing a high voltage blocking capability. For example, a MOS (“metal oxide semiconductor”) power transistor should, depending upon application requirements, be capable of blocking drain to source voltages Vds of some tens to some hundreds or thousands of volts. MOS power transistors typically conduct very large currents which may be up to some hundreds of Amperes at typical gate-source voltages of about 2 to 20 V.
Lateral power devices, in which current flow mainly takes place parallel to a main surface of a semiconductor substrate, are useful for integrated circuits in which further components, such as switches, bridges and control circuits are integrated.
For example, power transistors may be used in DC/DC or AC/DC converters to switch a current through an inductor, in these converters frequencies in a range from several kHz up to several MHz are employed. In order to reduce switching losses, attempts are being made to minimize capacitances in the power transistors. This in turn allows for accelerated switching capacity.
At higher currents problems may arise when the source and the drain regions are to be contacted from the first main surface, due to the limited possibilities of contacting the source and the drain regions. For these reasons, attempts are being made to provide a quasi-vertical semiconductor device.